Questions concerning Adobe Audition 2020

In order:

• Amazon subscription for Audition is essentially the same as Adobe direct subscription for it, only via a third party. Not sure why you'd want to do that, but hey...
• All versions contain those effects; they are basic.
• Yes, Audition can remove artifacts from music files. Yes it does an excellent job for the money. There is one better alternative if you want to do just that specifically, but it costs more, and doesn't do anywhere near as many other things as Audition does.
• The ease of removing artifacts depends entirely upon what you are trying to remove. Some things you can't remove - but no other software would remove them either. What it comes down to is that we can't answer that question without knowing what you want to do exactly.

You can have a free trial of Audition for a week, so you can try some of this for yourself. If you get stuck we can generally answer questions quite quickly, although often it helps if you can provide samples (you have to upload them somewhere like Dropbox and provide a link - you can't just place them on forum posts).